MILWAUKEE (AP) — For some Republican presidential candidates, the party's first three debates have been pivotal, giving their campaigns a quick boost or shaking their supporters.

Ben Carson isn't among them.

The famously mild-mannered Carson has largely avoided making headlines in the widely watched televised events, often willing to cede the spotlight to more verbose rivals and finding himself overshadowed in policy discussions. Yet the retired neurosurgeon's standing with voters in preference polls has only gotten better.

"The political language and the traditional prism through which we evaluate candidates essentially does not apply to Ben Carson," says Phil Musser, a Republican strategist.

It's unlikely Carson will again shrink into the background Tuesday when the eight leading GOP candidates meet in Milwaukee. Now viewed as a front-runner for the Republican nomination, Carson faces intense scrutiny about the veracity of his celebrated biography, which has been central to his connection with voters.

His campaign manager, Barry Bennett, says Carson is prepared to be far more aggressive in the debate and is "a lot more fired up" after facing days of questions about his past.

"He will vociferously stand up for himself," Bennett said. "He's not going to attack anybody. But if somebody goes after him, they're going to see a lot more 'back at 'em' than they ever saw before."

While pieces of Carson's background had been challenged earlier in the campaign, the questions ballooned last week after CNN reported it could not find friends or confidants to corroborate the story, told in his widely read autobiography, of his unsuccessfully trying to stab a close friend when he was a teenager.

Later in the week, Politico examined Carson's claim of having been offered a scholarship to attend the U.S. Military Academy, and The Wall Street Journal said it could not confirm anecdotes told by Carson about his high school and college years.

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In a GOP primary where bashing the media is in vogue, Carson could come out ahead if the moderators of Tuesday's debate on Fox Business Network are seen as unfairly piling on. Carson's campaign was active in the effort to change how the party's debates are run after several candidates expressed unhappiness with moderators from CNBC at an event two weeks ago.

Wisconsin Gov. Scott Walker, who participated in two GOP debates before dropping out of the race, said he hoped the event in his home state proves more substantive.

"It felt like being on 'The Jerry Springer Show,'" Walker said of the first debates, adding: "If they had folding chairs ready for us, I think they would have hoped we would have smacked each other in the head."

Should Carson find himself in such a debate, some Republicans say he must walk a fine line between defending himself and sticking with the calm and quiet demeanor that has so far been a draw for voters.

"Will viewers and voters see the unflappable surgeon they have been inclined to support or will a more combative Carson emerge?" said Matt Strawn, the former chairman of the Iowa Republican Party. "If the latter, his standing may well suffer if he appears to be yet another politician trying to out-outrage the others on stage."

Carson's response will likely be influenced by the way his rivals handle the matter. So far, most have sided with Carson, saying he's been unfairly treated by the media.

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"They went too far with Ben Carson," Kentucky Sen. Rand Paul said Monday. "It's just kind of silly. They are trying to paint it to his integrity, and I think that that's not fair."

The most likely candidate in the main event to challenge Carson is Donald Trump, although he said early Tuesday in a phone call to ABC's "Good Morning America" that he had no plans to zero in on Carson. "I have no idea what's going to happen, but it'll be interesting," he said.

If the billionaire real estate mogul stays silent, he'll do so after having previewed a potential line of attack at a rally in Springfield, Illinois, the night before, where he reviewed a long list of possible Carson exaggerations and unproven claims.

"With what's going on with this election, I've never seen anything like it. People are getting away with murder," Trump said. "If you try and hit your mother over the head with a hammer, your poll numbers go up. I never saw anything like it!"

Also in the main debate Tuesday are Marco Rubio and Ted Cruz, a pair of senators enjoying fresh momentum following their strong performances in the last contest; former Florida Gov. Jeb Bush, who is in the midst of an attempted campaign reset, and businesswoman Carly Fiorina and Ohio Gov. John Kasich.

Trump has recently stepped up his criticism of Rubio, calling him a "total lightweight" and "highly overrated politician" in tweets sent late Monday night.

Missing from the lineup are New Jersey Gov. Chris Christie and former Arkansas Gov. Mike Huckabee. Both were dropped from the top-tier debate with low poll numbers in national surveys, sparking criticism for the way networks hosting the debates have determined participation.

Christie and Huckabee will instead appear in an undercard debate, along with Louisiana Gov. Bobby Jindal and former Pennsylvania Sen. Rick Santorum.

"We're not whiners and moaners and complainers in the Christie campaign," Christie said on Fox News. "Give me a podium, give me a stage, put the camera on, we'll be just fine."

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Pace reported from Washington. Associated Press writers Brian Bakst in Minnesota, Jill Colvin in New Jersey and Steve Peoples in Milwaukee contributed to this report.